In a combustion engine, blow-by gases typically include unburned gasoline. That is, an amount of air and unburned gasoline from the engine cylinder is pulled past the piston rings and into the crankcase. Instead of exhausting such blow-by gases to the atmosphere, a positive crankcase ventilation (PCV) system recycles the blow-by gases through a PCV valve into the engine's intake manifold. Such recycling occurs when the engine is operating at relatively slow speeds (e.g. idling), i.e., when the air pressure in the crankcase is higher than the air pressure in the intake manifold.
One problem associated with PCV systems and their use involves oil vapors. An engine's crankcase is used to store oil. A pan located below the crankshaft holds oil, and generally oil vapors from the oil in the pan may find their way into the blow-by gases.
It is undesirable for oil to be recycled with blow-by gases into an engine's intake manifold. Such oil may degrade engine performance by lowering the overall octane of the combustion mixture in a cylinder. Such oil also may coat the air intake and prevent airflow.
To combat the presence of oil in blow-by gases, oil and air separators were developed to remove the oil from the blow-by gases before recirculation into the intake manifold. There are various different models or types of oil and air separators available. With all such systems, the intake side of the oil and air separator is connected to a vent or evacuation tube for the crankcase.
This approach to oil and air separation is not without its drawbacks, however. It would prove advantageous to eliminate the need for a separate vent or evacuation tube by using the engine oil fill port to exhaust blow-by gases from the crankcase.